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SignalingSignalingBasic Concepts of CCS Basic Concepts of CCS

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Overview

The relationship between signaling network and telecom network

The development of No.7 signaling system

The development goal of No.7 signaling system

The Development GoalThe general goal of the No.7 signaling system is to suggest an internationally standardized common channel signaling system with general applications fields so that the digital communication networks with digital SPC switches can work in the best status. Furthermore, such networks can provide sequential (Forming or characterized by a sequence)and highly reliable transmission with no loss and no repetition.

Signaling----Definition

It is the dialog language for the communication between various parts of the telecom network.

Working area

Subscriber signaling: Between sub. & switch

inter-office: Control the setup and release of call

Monitoring signals: Monitor the changes of call states or conditions in the lines

Selection signals ： Routing information

Operation signals: Management and maintenance of telecom networks

Signaling function

Signaling----Classification

Common Channel Signaling

Channel Associated Signaling ：

Transmitting path

Common Channel Signaling (CCS)

In telephony, Common Channel Signaling (CCS), in the US also Common Channel Interoffice Signaling (CCIS), is the transmission of signaling information (control information) on a separate channel from the data, and, more specifically, where that signaling channel controls multiple data channels…….

Channel Associated Signaling (CAS)

Channel Associated Signaling (CAS), also known as per-trunk signaling (PTS), is a form of digital communication signaling. As with most telecommunication signaling methods, it uses routing information to direct the payload of voice or data to its destination. With CAS signaling, this routing information is encoded and transmitted in the same channel as the payload itself.

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Exchange B

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ISDN ISDN line line

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ISDN ISDN line line

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Signaling Signaling terminalterminal

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Common Channel Signaling System

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Channel Associated Signaling

Advantages of CCSCompared with Channel Associated Signaling, Common Channel Signaling has many important advantages

Information can be switched between processors much faster than in channel-associated signaling.

With a huge signal capacity, it can hold dozens or even hundreds of different kinds of signals, thus providing more new services.

With a great flexibility, it can provide more new services simply by modifying software to increase signals.

Line signaling device is not needed any more at any trunk station, which shall greatly reduce investment costs.

Since line signaling is no longer needed, trunk devices can be used both in calls from A to B, and in calls from B to A.

In such bi-directional working modes, even less circuits are required than when trunk circuits are respectively used in single call directions.

When a call is being set up, signals related to this call can be sent. In this way, the subscriber can change the already setup connections. For example, the subscriber can transfer one call to another place, or request a third party to join the present connections.

Signals can be switched between processors so as to be used for maintenance or network management.

The No.7 line signaling can provide powerful support for ISDN, IN, TMN (telecommunication management Network)and cellular mobile communication systems, as this signaling is their basis.

Disadvantages of CCS The error rate of the common channel

signaling system must be very low. Its reliability must be much higher than

the channel associated signaling system. This is because once the data link fails, all related calls between the two related switches shall be affected.

Bi-directional trunk working modes exist conflict of seizure (A Sudden Disorder).

The SS7 systems that every transnational corporation produces are having some problems in compatibleness.

SS7 Protocol System Structure

SCCPMTP3 （ NETWORK LAYER ）

MTP2 （ DATA Link LAYER ）

MTP1 （ PHYSICAL LAYER ）

TUPISUP DUPUser Part

Message

Transfer

Part

ISUP (ISDN User Part): ISUP supports basic telephone call connect/disconnect between end offices. ISUP was derived from TUP, but supports ISDN and intelligent networking functions.

DUP (Data User part):DUP defines the necessary call control, and facility registration and cancellation related elements for international common channel signalling by use of SS7 for circuit-switched data transmission services.

TUP (Telephone User Part):TUP is an analog protocol that performs basic telephone call connect and disconnect.

User part

Signal network function

Signaling link function

Signaling data link function

L4

L3

L2

L1Physical path

Logical path

Logical path

Logical path

User part

Signal network function

Signaling link function

Signaling data link function

Example

The President of a Chinese company is communicating with the President of a Pakistani Company , however neither speaks the other’s language. Each employs an English translator and the translated messages are sent by the Fax operator over physical communication channel. Thus, the two presidents are communicating with each other through five layers below them

Company A(China)

physical communication channel

Company B (Pakistan)

Chinese President

Translator

Fax Operator

Write to paper

Print to paper

Pakistani President

Translator

Fax Operator

Write to paper

Print to paper

Effective Communication

Telegraph

The CCS network consists of the following parts Signaling point (SP)

It refers to the node in the signaling system that provides Common Channel Signaling. SP can also be divided into source points OPC (Originating Point Code)

The SP that generate signaling messages DPC (Destination Point Code)

The SP that receives signaling point code.

Common Channel Signaling Network

Signaling Transfer Point (STP)It refers to SP that transfer signaling messages from one signaling link to another. They are neither source points, nor destination points. That is, they are the middle node points during signaling transfer.

OPC or DPC is 14-bit address (24-bit for China

B

Voice channels

ASignaling link

C

2_2_2 3_3_3

OPC or DPC is not absolute. OPC and DPC are relative, the OPC of certain Office, for other Offices, is DPC.

For example, the SP of switch A is 2_2_2, and SP of switch B is 3_3_3. If you work in switch A then 2_2_2 is OPC for A, and 3_3_3 is DPC for A.

SIGNALING LINKIt refers to the signaling message channel that connects an SP and another SP( or STP).

SIGNALING LINK SETA bunch of signaling links directly connecting two SP

(including STP) form one signaling link set.

ROUTE One such set usually includes all parallel signaling

links.

ROUTE SET It is also possible to set several routes between two SP

LinkLink Set 1

Link Set 2

ROUTE1

ROUTE2

ROUTE3

ROUTE SET

B

Voice channels

ASignaling link

The Associated Mode

In this mode, Messages related to the voice channel connecting two switches are sent on the signaling link that directly connects two switches.

BVoice Channels

ASignaling link

C

The Quasi- Associated mode This can be called a special case of the non-associated mode. In this mode, signaling messages between switches A and B go through the several preset concatenated signaling links, but voice signals go through the direct channels between A and B. Normally, different transmission carriers are used in the common channel signaling systems and their related voice links.

The 1st level defines the physical, electrical, and functional features of the signaling data link, and is thus similar to the OSI physical layer. It determines the connection method with the data link, and provides an information carrier for the signaling link. In digital transmission, signaling data links are usually digital channels at 64kbit/s.

Functions of Signaling Data Link Level

Functions of the Signaling Link Level

The second level defines the signaling message transmission functions and procedure related to its transfer on a signaling data link. The second level and the first signaling data link used as a whole as an information carrier, provide a signaling link between two signaling points for the reliable transfer of messages.

Error check 16 bit Check Code

Error Correction FSN, BSN, FIB, BIB, Basic Error Correction

and Preventive Cyclic Retransmission (PCR) Error Monitoring of Signaling Link

Prevents the retransmission when error occurs

Flow Control Prevent the link congestion if the load on

the link is too heavy

The Signaling Network Level

Within a signaling network, each switching node is allocated a signaling point code, which is 14-bit address (24-bit for China). Every CCITT No.7 message then contains the point code of the originating node (OPC) and the destination point code or( DPC).

Message Routing Selecting the signaling link that is used by

each signaling message to be transmitted Message Distribution

Send the message to a user part or level-3functions after receiving the message

Message Authentication To determine whether a signaling point is

the destination point of a message after the signaling point receives the message.

The User Part The user part is the fourth function

level of the NO.7 signaling system. Its main function is to control the setup and release of various basic calls.

The major user parts include the telephone user part (TUP), the ISDN user part (ISUP) and the signaling connection control part (SCCP)

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